Mycobacterium leprae is an obligate intracellular parasite that serves as the etiologic agent of leprosy, a disease that afflicts some 15 million individuals worldwide. M. leprae is capable of multiplication in macrophages and can invade and multiply in the Schwann cells of the peripheral nervous system. Studies are proposed that will lead to an understanding of the genes and gene products of M. leprae that are important in the pathogenicity of this organism through molecular and functional analyses of recombinant molecules from genomic libraries. Specifically, we will (1) isolate and characterize the gene for manganese superoxide dismutase, an enzyme likely to be important in cellular defense against oxygen toxicity; (2) quantitate the amounts of DNA, ribosomal RNA (rRNA) and messenger RNA (mRNA) in M. leprae cells using specific DNA probes for each kind of nucleic acid; (3) study the activity of M. leprae genes in response to phagocytosis by and during existence in macrophages; (4) quantitate the amounts of DNA, rRNA and mRNA in M. leprae at different states during growth of the bacilli in mouse footpads; and (5) develop methodology for detecting submicroscopic amounts of M. leprae cells in human infections, using the polymerase chain reaction in conjunction with an M. leprae-specific repeated DNA sequence probe. The studies will make use of the technologies of molecular biology, microbial genetics, microbiology, immunology, and biochemistry.